Balloon angioplasty is utilized to treat coronary arteries narrowed by plaque deposits. A catheter having an inflatable balloon secured to its distal end is advanced through the artery to the narrowed region. The balloon is inflated, causing the narrowed, or stenosed, region of the artery to be expanded. The balloon is then deflated and withdrawn.
A serious problem associated with balloon angioplasty has been the occurrence in up to 30% of the cases of so-called restenosis, either immediately after the procedure or within about six months. Immediate restenosis, also known as abrupt reclosure, results from flaps or segments of plaque and plaque-ridden tissue which are formed during balloon angioplasty and which can block the artery. Such blockage of the artery requires emergency surgery and often results in death. Furthermore, a surgical team is required to stand by during the balloon angioplasty procedure. Restenosis at a later time results from causes that are not totally known. Thrombus formation is believed to play an important part. Often, repeat balloon angioplasty or surgery is required, and another episode of restenosis may occur.
One approach to dealing with the problem of restenosis is to maintain a passage through the artery with an endovascular stent. The stent is a generally tubular device which is placed inside the blood vessel after balloon angioplasty or some other type of angioplasty has been completed. The stent has sufficient strength and resiliency to resist restenosis and to maintain a passage through the vessel. A catheter is typically used to deliver the stent to the stenosed site. U.S. Pat. No. 4,733,665, issued Mar. 29, 1988 to Palmaz, discloses a vascular stent comprising an expandable wire mesh tube. The stent is positioned over an inflatable balloon secured to a catheter and is advanced to the stenosed region. The balloon is inflated, thereby expanding the stent into contact with the vessel wall. The elastic limit of the wire mesh is exceeded when the balloon is expanded, so that the stent retains its expanded configuration. U.S. Pat. No. 4,503,569, issued Mar. 12, 1985 to Dotter, discloses a shape memory alloy stent that is advanced to a stenosed region on a catheter. The stent has the form of a coil spring. After positioning, the stent is heated with a hot fluid causing the shape memory alloy to expand into contact with the blood vessel. U.S. Pat. No. 4,740,207, issued Apr. 26, 1988 to Kreamer, discloses a plastic graft for repair of the vascular system. A catheter is suggested for placement of the graft in a coronary artery. Stents for placement in blood vessels are also disclosed in U.S. Pat. No. 4,553,545, issued Nov. 19, 1985 to Maass et al and U.S. Pat. No. 4,732,152, issued Mar. 22, 1988 to Wallsten et al. U.S. Pat. No. 4,577,631 issued Mar. 25, 1986 to Kreamer, discloses a Dacron blood vessel graft that is coated with an adhesive. The Kreamer patent states that the adhesive may be activated by ultraviolet or ultrasonic energy after placement in the aorta.
All known prior art vascular stents have been fabricated of metal or plastic and remain in the blood vessel indefinitely. The long term effects of such devices are not well known. Furthermore, such devices have a fixed range of expansion within the blood vessel. In some cases, the stent may be too small in diameter, even after expansion, to be affixed to the vessel wall, and in other cases the stent may expand to such a diameter that the vessel is damaged or ruptured. In either case, improperly sized or positioned prior art stents require surgery for removal.
It has been proposed in the prior art to use collagens and collagen-based compositions in skin grafts, bandages and vascular prostheses. An advantage of using collagen in such devices is that collagen occurs naturally in the human body, and the graft or prosthesis is eventually absorbed into the tissue to which it is attached. U.S. Pat. No. 4,319,363, issued Mar. 16, 1982 to Ketharanathan, discloses a vascular prosthesis for use as a surgical graft. The prosthesis comprises a tubular wall of Type I collagenous tissue. U.S. Pat. No. 4,390,519, issued Jun. 28, 1983 to Sawyer, discloses a bandage wherein a collagen or collagen-like substance is incorporated into the pad or sponge of the bandage. U.S. Pat. No. 4,642,118, issued Feb. 10, 1987 to Kuroyanagi et al, discloses a man-made skin including a collagen sponge layer and a poly-alpha-amino acid membrane. U.S. Pat. No. 3,808,113, issued Apr. 30, 1974 to Okamura et al discloses a method for manufacturing medical articles comprising a polymer coated with collagen. In one step of the process, the collagen is irradiated with radioactive rays, an electron beam or ultraviolet radiation to fix the collagen layer.
U.S. Pat. No. 4,417,576, issued Nov. 29, 1983 to Baran, discloses a double wall surgical cuff for introduction into a body passage. The outer cuff is porous, and a sponge material is positioned between the inner and outer cuffs. A surgical fluid such as an anesthetic is absorbed by the sponge material. When the inner cuff is inflated, the fluid is driven through the porous outer cuff to the walls of the body passage.
It is a general object of the present invention to provide improved endovascular stents.
It is another object of the present invention to provide a collagen-based endovascular stent or to use collagen as a temporary adhesive until the body incorporates it.
It is another object of the present invention to provide an endovascular stent that is formed into its final configuration at a site in a blood vessel where it is to be placed.
It is a further object of the present invention to provide methods and apparatus for delivery and placement of a collagen-based endovascular stent.
It is yet another object of the present invention to provide an endovascular stent which is crosslinked into its final configuration in a blood vessel by application of energy.
It is still another object of the present invention to provide an endovascular stent that is formed in place by the application of laser energy to a collagen-based material.